can't auto-provision Grandstream BLF

I have the 3cx paid version 10, a mess of Grandstream 2120 / 1450, and though the phones nicely auto-provision in terms of extension and authentication info, I am unable to get the phones to reflect the BLF config that I set on 3cx's "Phone Provisioning" tab.

I have very carefully followed the appropriate Grandstream setup guide, without success. I can manually set the function of the phones "Multi Purpose Key" to act as BLF for other extensions within the phones web UI, and it works just fine. The manual setting isn't removed if I reprovision the phone from within 3cx.

Can you provide more details about the issue?
Basically, you are not able to auto-provision the BLF on the phones from 3CX provisioning module?
Can you post a screenshot from this tab? (Make sure to hide personnal info such as MAC address from screenshot)
Can you submit a ticket on http://www.grandstream.com/support/submit-a-ticket since some traces and templates used may be needed?